US20220169509A1 - Method for producing sulfide solid electrolyte - Google Patents

Method for producing sulfide solid electrolyte Download PDF

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US20220169509A1
US20220169509A1 US17/434,876 US202017434876A US2022169509A1 US 20220169509 A1 US20220169509 A1 US 20220169509A1 US 202017434876 A US202017434876 A US 202017434876A US 2022169509 A1 US2022169509 A1 US 2022169509A1
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homogeneous solution
organic solvent
solution
slurry
solid electrolyte
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US12103848B2 (en
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Tomohiro Ito
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Mitsubishi Gas Chemical Co Inc
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B25/00—Phosphorus; Compounds thereof
    • C01B25/14—Sulfur, selenium, or tellurium compounds of phosphorus
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B17/00—Sulfur; Compounds thereof
    • C01B17/22—Alkali metal sulfides or polysulfides
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B13/00—Apparatus or processes specially adapted for manufacturing conductors or cables
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0561—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of inorganic materials only
    • H01M10/0562—Solid materials
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/70—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
    • C01P2002/72—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data by d-values or two theta-values, e.g. as X-ray diagram
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/40—Electric properties
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2300/00—Electrolytes
    • H01M2300/0017—Non-aqueous electrolytes
    • H01M2300/0065—Solid electrolytes
    • H01M2300/0068—Solid electrolytes inorganic
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present invention relates to a method for producing a sulfide-based solid electrolyte.
  • the sulfide has characteristics that it has high ion conductivity and is relatively soft, and that it is easy to form the interface between solids.
  • the sulfide is stable with respect to active materials and has been developed as a practical solid electrolyte.
  • Non-Patent Document 1 Non-Patent Document 2
  • SiS 2 which is a sulfide of Si, is often used as a raw material.
  • SiS 2 has high reactivity with the atmosphere and contains an oxygen-containing compound, and often contains Si that is an unreacted raw material, and therefore it is difficult to prepare SiS 2 not containing impurities.
  • Non-Patent Document 1 Acta Cryst. (2015). B71, 727-736
  • Non-Patent Document 2 Nature Energy 1, Article number: 16030 (2016)
  • the present inventors diligently made researches in consideration of the above-described problems and obtained an unexpected finding that a sulfide-based solid electrolyte with little impurities that is stable can be produced by using, as a raw material, an Li—Si—S homogeneous solution which contains at least elemental lithium (Li), elemental silicon (Si) and elemental sulfur (S) in an organic solvent.
  • an Li—Si—S homogeneous solution which contains at least elemental lithium (Li), elemental silicon (Si) and elemental sulfur (S) in an organic solvent.
  • the present invention is as described below.
  • a method for producing a sulfide-based solid electrolyte comprising:
  • a solution making step 1 in which Li 2 S and P 2 S 5 are mixed with each other in an organic solvent so that the Li 2 S/P 2 S 5 molar ratio becomes from 0.7 to 1.5 to prepare an Li—P—S homogeneous solution;
  • a slurry forming step in which the homogeneous mixed solution and Li 2 S are mixed with each other to prepare a slurry
  • a heat treatment step in which the precursor is heated at 200 to 700° C. to obtain a sulfide-based solid electrolyte.
  • ⁇ 2> The method according to item ⁇ 1>, wherein the solution making step 2 comprises adding Li 2 S and SiS 2 to the organic solvent to be mixed therewith to prepare the Li—Si—S homogeneous solution.
  • the solution making step 2 comprises adding Li 2 S and SiS 2 to the organic solvent to be mixed therewith and filtering the mixture to prepare the Li—Si—S homogeneous solution.
  • ⁇ 4> The method according to any one of items ⁇ 1> to ⁇ 3>, wherein the organic solvent in the solution making step 1 and the solution making step 2 is at least one selected from the group consisting of tetrahydrofuran, acetonitrile, ethyl acetate and methyl acetate.
  • the solution mixing step comprises further adding lithium halide to prepare the homogeneous mixed solution.
  • a method for producing a sulfide-based solid electrolyte the method comprising:
  • a slurry forming step 1 in which an Li 3 PS 4 -containing slurry is prepared; a solution making step in which an Li—Si—S homogeneous solution, which contains at least elemental lithium (Li), elemental silicon (Si) and elemental sulfur (S) in an organic solvent, is prepared;
  • a slurry forming step 2 in which the Li 3 PS 4 -containing slurry and the Li—Si—S homogeneous solution are mixed with each other to prepare a mixed slurry;
  • a slurry forming step 3 in which the mixed slurry and Li 2 S are mixed with each other to prepare a slurry
  • a heat treatment step in which the precursor is heated at 200 to 700° C. to obtain a sulfide-based solid electrolyte.
  • the slurry forming step 1 comprises mixing Li 2 S and P 2 S 5 with each other in an organic solvent so that the Li 2 S/P 2 S 5 molar ratio becomes from 0.7 to 1.5 to prepare an Li—P—S homogeneous solution and mixing the Li—P—S homogeneous solution and Li2S with each other to prepare an Li 3 PS 4 -containing slurry.
  • the solution making step comprises adding Li 2 S and SiS 2 to the organic solvent to be mixed therewith to prepare the Li—Si—S homogeneous solution.
  • the solution making step comprises adding Li 2 S and SiS 2 to the organic solvent to be mixed therewith and filtering the mixture to prepare the Li—Si—S homogeneous solution.
  • the organic solvent in the solution making step is at least one selected from the group consisting of tetrahydrofuran, acetonitrile, ethyl acetate and methyl acetate.
  • the slurry forming step 2 comprises further adding lithium halide to prepare the mixed slurry.
  • ⁇ 12> The method according to any one of items ⁇ 1> to ⁇ 11>, wherein the temperature in the drying step is 60 to 280° C. ⁇ 13>
  • the present invention it is possible to provide a method for producing a sulfide-based solid electrolyte with little impurities providing stable performance, which has excellent productivity. Further, according to the present invention, it is possible to provide a formed body obtained by heating and forming the sulfide-based solid electrolyte and an all-solid-state battery comprising the sulfide-based solid electrolyte. Moreover, this production method can be applied to mass production.
  • FIG. 1 is a schematic view showing a crystal structure of a sulfide-based solid electrolyte according to one embodiment of the present invention.
  • FIG. 2 is a schematic cross sectional view of an all-solid-state battery according to one embodiment of the present invention.
  • FIG. 3 is a graph showing the results of the X-ray diffraction measurement of the sulfide-based solid electrolytes obtained in Examples 1-3 and Comparative Example 1.
  • FIG. 4 is a graph showing the results of the X-ray diffraction measurement of the filter residue and the white solid obtained in ⁇ Solution making step 2> of Example 1.
  • the first embodiment of the present invention is a method for producing a sulfide-based solid electrolyte, the method including:
  • a solution making step 1 in which Li 2 S and P 2 S 5 are mixed with each other in an organic solvent so that the Li 2 S/P 2 S 5 molar ratio becomes from 0.7 to 1.5 to prepare an Li—P—S homogeneous solution;
  • a slurry forming step in which the homogeneous mixed solution and Li 2 S are mixed with each other to prepare a slurry
  • a heat treatment step in which the precursor is heated at 200 to 700° C. to obtain a sulfide-based solid electrolyte.
  • the Li—P—S homogeneous solution is defined as a solution which contains at least elemental lithium (Li), elemental phosphorus (P) and elemental sulfur (S) in an organic solvent, wherein no undissolved substance is precipitated
  • the Li—Si—S homogeneous solution is defined as a solution which contains at least elemental lithium (Li), elemental silicon (Si) and elemental sulfur (S) in an organic solvent, wherein no undissolved substance is precipitated.
  • the solution making step 1 is a step in which Li 2 S and P 2 S 5 are mixed with each other in an organic solvent so that the Li 2 S/P 2 S 5 molar ratio becomes from 0.7 to 1.5 to prepare an Li—P—S homogeneous solution.
  • the reaction slowly proceeds even at room temperature, but heating can be performed for increasing the reaction rate.
  • heating it is sufficient when it is performed at a temperature that is the boiling point of the organic solvent or lower.
  • the temperature varies depending on the organic solvent to be used, but is usually lower than 120° C. Heating can also be performed under the pressurized state using an autoclave or the like.
  • a high temperature 120° C. or higher
  • the reaction time in the solution making step 1 varies depending on the type of the organic solvent and the particle diameter and concentration of raw materials, but for example, by performing the reaction for 0.1 to 24 hours, the reaction is completed and a solution can be made.
  • the Li—P—S homogeneous solution is produced by mixing Li 2 S and P 2 S 5 with each other in the organic solvent so that the Li 2 S/P 2 S 5 molar ratio becomes from 0.7 to 1.5 to cause a reaction.
  • the Li 2 S/P2S 5 molar ratio is 0.7 to 1.5, a solution can be made from Li 2 S and P 2 S 5 at room temperature.
  • precipitation may occur.
  • This solution may contain unreacted Li 2 S and P 2 S 5 . Further, the solution may contain impurities derived from Li 2 S and P 2 S 5 . The impurities are scarcely dissolved in the solvent and most of them precipitate. For this reason, it is preferred to apply filtration or centrifugation to the obtained solution to remove the precipitate and separate the solution, thereby obtaining a high-purity Li—P—S homogeneous solution.
  • P 2 S 5 a synthesized product or commercially-available product can be used.
  • the particle diameter is preferably 10 nm to 100 ⁇ m, more preferably 100 nm to 30 ⁇ m, and particularly preferably 300 nm to 10 ⁇ m.
  • the content is more preferably 300 ppm or less, and particularly preferably 50 ppm or less.
  • the solution making step 2 is a step in which an Li—Si—S homogeneous solution, which contains at least elemental lithium (Li), elemental silicon (Si) and elemental sulfur (S) in an organic solvent, is prepared.
  • Li—Si—S homogeneous solution which contains at least elemental lithium (Li), elemental silicon (Si) and elemental sulfur (S) in an organic solvent.
  • SiS 2 As a starting material, it is difficult to homogeneously disperse Si in a solid electrolyte at the time of synthesis. Further, SiS 2 has high reactivity with the atmosphere and often contains an oxygen-containing compound or Si that is an unreacted raw material. For such reasons, it is difficult to prepare SiS 2 not containing impurities. Further, it is difficult to remove these impurities from SiS 2 .
  • Si is easily dispersed homogeneously in the solid electrolyte at the time of synthesis and a side reaction is not easily caused because of little impurities. For this reason, it is considered that a sulfide-based solid electrolyte having high ion conductivity can be stably produced by using it.
  • the Li—Si—S homogeneous solution in which Li, Si and S are dissolved, is provided by mixing Li 2 S and SiS 2 with each other in an organic solvent so that the Li 2 S/SiS 2 molar ratio becomes from 0.3 to 1.0 to cause a reaction.
  • This solution may contain unreacted Li 2 S and SiS 2 . Further, the solution may contain impurities derived from Li 2 S and SiS 2 .
  • the solution obtained is subjected to filtration or centrifugation to remove the precipitate and separate the solution, thereby obtaining the Li—Si—S homogeneous solution.
  • concentration of each element in the obtained homogeneous solution is analyzed by means of ICP.
  • the precipitate can be removed by means of filtration or centrifugation.
  • the pore size of the filter is desirably 10 ⁇ m or less.
  • the pore size is more preferably 5 ⁇ m or less, and particularly preferably 2 ⁇ m or less.
  • the precipitate obtained includes unreacted raw materials such as Li 2 S and SiS 2 and impurities derived from SiS 2 .
  • the impurities include oxygen-containing compounds of Si or SiS 2 and SiO 2 .
  • Li 2 S a synthesized product or commercially-available product can be used.
  • the content is more preferably 300 ppm or less, and particularly preferably 50 ppm or less.
  • the particle diameter is preferably 10 nm to 100 ⁇ m, more preferably 100 nm to 30 ⁇ m, and particularly preferably 300 nm to 10 ⁇ m. Note that the particle diameter can be measured by means of SEM, a particle size distribution measurement apparatus utilizing laser scattering, or the like.
  • SiS 2 a synthesized product or commercially-available product can be used.
  • the particle diameter is preferably 10 nm to 100 ⁇ m, more preferably 100 nm to 30 ⁇ m, and particularly preferably 300 nm to 10 ⁇ m.
  • the particle diameter can be measured by means of SEM, a particle size distribution measurement apparatus utilizing laser scattering, or the like. Note that there is no problem even when a part of the above-described raw materials to be used are amorphous.
  • the content is more preferably 300 ppm or less, and particularly preferably 50 ppm or less.
  • the organic solvent is not particularly limited as long as it does not react with Li 2 S or SiS 2 .
  • examples thereof include an ether-based solvent, an ester-based solvent, a hydrocarbon-based solvent and a nitrile-based solvent.
  • Specific examples thereof include tetrahydrofuran, cyclopentyl methyl ether, diisopropyl ether, diethyl ether, dimethyl ether, dioxane, methyl acetate, ethyl acetate, butyl acetate and acetonitrile.
  • At least one selected from the group consisting of tetrahydrofuran, acetonitrile, ethyl acetate and methyl acetate is preferred, and acetonitrile is particularly preferred.
  • the moisture content it is preferably 100 ppm or less, and more preferably 50 ppm or less.
  • the organic solvent to be used in the solution making step 1 the same materials as above can be preferably used.
  • the total concentration of Li, Si and S in the organic solvent is preferably 0.5 to 20% by weight, more preferably 1 to 15% by weight, and particularly preferably 2 to 10% by weight.
  • the total concentration of Li, Si and S in the organic solvent is higher than 20% by weight, it is difficult to obtain a homogeneous solution because of precipitation of solids.
  • the total concentration of Li, Si and S in the organic solvent is lower than 0.5% by weight, a large amount of the organic solvent must be used and a load of solvent recovery is increased. In addition, it causes excessive increase in the size of a reactor.
  • the solution mixing step is a step in which the Li—P—S homogeneous solution and the Li—Si—S homogeneous solution are mixed with each other to prepare a homogeneous mixed solution.
  • the homogeneous mixed solution By adding the Li—P—S homogeneous solution to the Li—Si—S homogeneous solution, the homogeneous mixed solution can be prepared.
  • the P/Si molar ratio is preferably from 0.7 to 1.5.
  • the molar ratio is within the above-described range, a sulfide-based solid electrolyte exhibiting high ion conductivity tends to be obtained.
  • the type and concentration of elements can be confirmed, for example, by using an ICP emission spectrometer. Since performances of the sulfide-based solid electrolyte significantly change due to slight deviation of the composition, it is preferred that the elemental composition is accurately controlled by subjecting the homogeneous solution to ICP emission spectrometry.
  • a halogen compound can be added thereto.
  • the halogen compound is also dissolved in the organic solvent.
  • Preferred specific examples of the halogen compound include LiCl, LiBr, LiI, PCl 5 , PCl 3 , PBr 5 and PBr 3 , and more preferred are LiCl, LiBr and LiI. These materials may be used solely, or two or more of them may be used in combination.
  • the slurry forming step is a step in which the homogeneous mixed solution obtained in the solution mixing step and Li 2 S are mixed with each other to prepare a slurry.
  • mixing using an ordinary stirring blade is sufficient.
  • a homogenizer or an ultrasonic disperser may also be used.
  • the elemental composition ratio varies depending on elements to be used and there is a composition in which halogen is contained, but a composition by which an LGPS crystal is formed is more preferred.
  • Si-containing LGPS-based solid electrolytes for example, Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 , Li 10 (Si 0.5 Ge 0.5 )P 2 S 12 , Li 10 (Si 0.5 Sn 0.5 )P 2 S 12 , Li 10.35 Si 1.35 P 1.65 S 12 , Li 9.42 Si 1.02 P 2.1 S 9.96 O 2.04 , etc. are known.
  • the LGPS type crystal structure has an octahedron O composed of elemental Li and elemental S, a tetrahedron T 1 composed of at least one element selected from the group consisting of P, Ge, Si and Sn and elemental S, and a tetrahedron T 2 composed of elemental P and elemental S (PS 4 3 ⁇ anion), wherein the tetrahedron T 1 and the octahedron O share an edge and the tetrahedron T 2 and the octahedron O share an apex.
  • a solid electrolyte having the LGPS type crystal structure is more preferred because ion conductivity thereof is particularly high.
  • the mixing time after the additional addition of Li 2 S is preferably 0.1 to 24 hours, and more preferably 4 to 12 hours. Note that Li 2 S additionally added reacts with Li 2 S—P 2 S 5 in a solution state to produce Li 3 PS 4 , but when the reaction time is long, a large amount of Li 3 PS 4 is produced and an impurity layer is produced in a final product.
  • the temperature at the time of mixing may be room temperature. Heating may be performed, but when the temperature is too high, there is concern that a side reaction may proceed. When heating is performed, it is sufficient when it is performed at a temperature that is equal to or lower than the boiling point of the organic solvent.
  • the temperature varies depending on the organic solvent to be used, but is usually lower than 120° C.
  • Mixing in the slurry forming step is preferably performed under inert gas atmosphere.
  • the inert gas include nitrogen, helium and argon, and particularly preferred is argon.
  • the concentration of each of oxygen and moisture in the inert gas is preferably 1000 ppm or less, more preferably 100 ppm or less, and particularly preferably 10 ppm or less.
  • the drying step is a step in which the obtained slurry is dried to remove the organic solvent, thereby obtaining a precursor. Drying is preferably carried out by means of heated-air drying or vacuum drying under inert gas atmosphere.
  • the drying temperature is preferably 60 to 280° C., and more preferably 100 to 250° C.
  • the optimum temperature range slightly varies depending on the type of the organic solvent, but the temperature range is important.
  • the drying temperature is set to be too high in a state where the organic solvent exists, the quality of the precursor changes in almost all cases.
  • the drying temperature is too low, the amount of the residual solvent is larger, and when the next heat treatment step is directly carried out, the organic solvent is carbonized and a sulfide-based solid electrolyte obtained has high electron conductivity.
  • the solid electrolyte has electron conductivity depending on the method for using it, but the solid electrolyte to be used for the portion 2 in FIG. 2 is required to have sufficiently low electron conductivity. In the case of using the solid electrolyte for such applications, the amount of the residual solvent must be decreased as much as possible.
  • the drying time slightly varies depending on the type of the organic solvent and the drying temperature, but the organic solvent can be sufficiently removed by drying for 1 to 24 hours. Note that by removing the organic solvent under reduced pressure as in the case of vacuum drying, and by flowing an inert gas such as nitrogen and argon in which the moisture content is sufficiently low, the temperature at the time of removing the organic solvent can be lowered and the required time can be shortened.
  • the heat treatment step is a step in which the precursor obtained in the drying step is heated at 200 to 700° C. to obtain a sulfide-based solid electrolyte.
  • the heating temperature varies depending on the type, and in the case of a precursor containing Ge, Si or Sn, usually, the heating temperature is preferably 200 to 700° C., more preferably 350 to 650° C., and particularly preferably 400 to 600° C. When the temperature is lower than the above-described range, desired crystals are not easily generated, and when the temperature is higher than the above-described range, crystals other than those desired may be generated.
  • the heating time slightly varies depending on the heating temperature, but usually, crystallization can be sufficiently performed when the heating time is 0.1 to 24 hours. It is not preferred that heating is carried out at a high temperature for a long period of time which exceeds the above-described range because there is concern for change in quality of the sulfide-based solid electrolyte.
  • Heating can be performed under vacuum or inert gas atmosphere, but preferably performed under inert gas atmosphere.
  • inert gas nitrogen, helium, argon or the like can be used, and among them, argon is preferred.
  • the contents of oxygen and moisture are preferably low, and conditions thereof are the same as those at the time of mixing in the slurry forming step.
  • the second embodiment of the present invention is a method for producing a sulfide-based solid electrolyte, the method including:
  • Li—Si—S homogeneous solution which contains at least elemental lithium (Li), elemental silicon (Si) and elemental sulfur (S) in an organic solvent, is prepared;
  • a slurry forming step 2 in which the Li 3 PS 4 -containing slurry and the Li—Si—S homogeneous solution are mixed with each other to prepare a mixed slurry;
  • a slurry forming step 3 in which the mixed slurry and Li 2 S are mixed with each other to prepare a slurry
  • a heat treatment step in which the precursor is heated at 200 to 700° C. to obtain a sulfide-based solid electrolyte.
  • the slurry forming step 1 in the second embodiment is not particularly limited as long as the Li 3 PS 4 -containing slurry can be prepared thereby, but it is preferred to mix Li 2 S and P 2 S 5 with each other in an organic solvent so that the Li 2 S/P 2 S 5 molar ratio becomes from 0.7 to 1.5 to prepare an Li—P—S homogeneous solution and to mix the Li—P—S homogeneous solution and Li 2 S with each other, thereby preparing the Li 3 PS 4 -containing slurry.
  • the Li—Si—S homogeneous solution it is sufficient when the Li—Si—S homogeneous solution is used, and a reaction apparatus and conditions are not particularly limited.
  • a reaction apparatus and conditions are not particularly limited.
  • the method for producing the sulfide-based solid electrolyte from raw materials for example, solid phase synthesis according to a mechanical milling method using a planetary ball mill, liquid phase synthesis in which a raw material composition is reacted in the presence of an organic solvent, melt mixing described in Japanese Patent No. 5187703, etc. can be employed.
  • the sulfide-based solid electrolyte of the present invention obtained in the above-described manner can be formed into a desired formed body by various means and can be used for various applications including an all-solid-state battery described below.
  • the forming method is not particularly limited. For example, a method similar to the method for forming respective layers constituting the all-solid-state battery described in ⁇ All-solid-state battery> below can be used.
  • the sulfide-based solid electrolyte of the present invention can be used, for example, as a solid electrolyte for all-solid-state batteries. Further, according to another embodiment of the present invention, an all-solid-state battery comprising the above-described solid electrolyte for all-solid-state batteries is provided.
  • the “all-solid-state battery” is an all-solid-state lithium ion secondary battery.
  • FIG. 2 is a schematic cross sectional view of an all-solid-state battery according to one embodiment of the present invention.
  • An all-solid-state battery 10 has a structure in which a solid electrolyte layer 2 is arranged between a positive electrode layer 1 and a negative electrode layer 3 .
  • the all-solid-state battery 10 can be used in various devices including mobile phones, personal computers and automobiles.
  • the sulfide-based solid electrolyte of the present invention may be contained as a solid electrolyte in at least one of the positive electrode layer 1 , the negative electrode layer 3 and the solid electrolyte layer 2 .
  • the sulfide-based solid electrolyte of the present invention is contained in the positive electrode layer 1 or negative electrode layer 3
  • the sulfide-based solid electrolyte of the present invention is used in combination with a publicly-known positive electrode active material or negative electrode active material for lithium ion secondary batteries.
  • the quantitative ratio of the sulfide-based solid electrolyte of the present invention to be contained in the positive electrode layer 1 or negative electrode layer 3 is not particularly limited.
  • the sulfide-based solid electrolyte of the present invention may be used solely, or according to need, may be suitably used in combination with an oxide solid electrolyte (e.g., Li 7 La 3 Zr 2 O 12 ), a sulfide-based solid electrolyte (e.g., Li 2 S—P 2 S 5 ), other complex hydride solid electrolytes (e.g., LiBH 4 and 3LiBH 4 —LiI), etc.
  • oxide solid electrolyte e.g., Li 7 La 3 Zr 2 O 12
  • a sulfide-based solid electrolyte e.g., Li 2 S—P 2 S 5
  • other complex hydride solid electrolytes e.g., LiBH 4 and 3LiBH 4 —LiI
  • the all-solid-state battery is prepared by forming and layering the above-described layers, and the forming method and layering method for the respective layers are not particularly limited.
  • Examples thereof include: a method in which a solid electrolyte and/or an electrode active material are dispersed in a solvent to provide a slurry-like mixture, which is applied by a doctor blade, spin coating or the like and subjected to rolling to form a film; a gas phase method in which film forming and layering are performed by using a vacuum deposition method, ion plating method, sputtering method, laser ablation method or the like; and a pressing method in which powder is formed by hot pressing or cold pressing (not heating) and layering is performed.
  • the sulfide-based solid electrolyte of the present invention is relatively soft, it is particularly preferred to prepare the all-solid-state battery by forming the respective layers by means of the pressing method and layering the layers.
  • the pressing method there are hot pressing in which heating is performed and cold pressing in which heating is not performed, but forming the layers can be sufficiently carried out even by means of cold pressing.
  • the present invention includes a formed body obtained by heating and forming the sulfide-based solid electrolyte of the present invention.
  • the formed body is suitably used as the all-solid-state battery.
  • the present invention includes a method for producing an all-solid-state battery, which includes a step of heating and forming the sulfide-based solid electrolyte of the present invention.
  • Li 2 S manufactured by Sigma-Aldrich, purity: 99.8%
  • P 2 S 5 manufactured by Sigma-Aldrich, purity: 99%
  • Li 2 S manufactured by Sigma-Aldrich, purity: 99.8%
  • SiS 2 manufactured by Mitsuwa Chemicals Co., Ltd.
  • these materials were added to 610 g of acetonitrile (manufactured by Wako Pure Chemical Industries, Ltd., super dehydrated grade) so that the concentration of (Li 2 S+SiS 2 ) became 3 wt %, and mixing was carried out at room temperature for 24 hours. The mixture was gradually dissolved, but at this stage, impurities in the raw materials remained.
  • Li—Si—S homogeneous solution was filtered with a membrane filter (PTFE, pore size: 1.0 ⁇ m), thereby obtaining 2.0 g of a filter residue and 578 g of a filtrate (Li—Si—S homogeneous solution).
  • Li/Si molar ratio
  • concentration of (Li 2 S+SiS 2 ) was 3.07 wt %.
  • Li 2 S Li 2 S was added while stirring so that the amount thereof became 6.27 times the molar quantity of P 2 S 5 , and mixing was carried out at room temperature for 12 hours to prepare a slurry.
  • the series of operations was carried out in the glovebox under argon atmosphere.
  • Li 2 S:P 2 S 5 :SiS 2 was 6.27:1:1.64.
  • the obtained slurry was dried under vacuum at 180° C. for 4 hours to remove the solvent. Removal of the solvent was carried out while stirring the solution. After that, it was cooled to room temperature to obtain a precursor.
  • the obtained precursor was put into a glass reaction tube, which was placed in an electric tube furnace in a manner such that the precursor was not exposed to atmosphere.
  • Argon (G3 grade) was injected into the reaction tube, the temperature was increased to 550° C. over 3 hours, and then burning was carried out at 550° C. for 8 hours, thereby synthesizing Li 3.45 Si 0.45 P 0.55 S 4 crystal.
  • Li 2 S manufactured by Sigma-Aldrich, purity: 99.8%
  • P 2 S 5 manufactured by Sigma-Aldrich, purity: 99%
  • Li—P—S homogeneous solution 8.29 g of the Li—P—S homogeneous solution was mixed with 23.30 g of the Li—Si—S homogeneous solution so that the molar ratio of Si:P became 1:1 to prepare a homogeneous mixed solution. Further, to the obtained homogeneous mixed solution, 51.9 mg of LiCl (manufactured by Sigma-Aldrich, purity: 99.99%), wherein the amount thereof was 0.40 time the molar quantity of P 2 S 5 in the homogeneous mixed solution, was added while stirring, and mixing was carried out at room temperature for 3 hours.
  • LiCl manufactured by Sigma-Aldrich, purity: 99.99%
  • Li 2 S Li 2 S was added while stirring so that the amount thereof became 6.45 times the molar quantity of P 2 S 5 , and mixing was carried out at room temperature for 12 hours to prepare a slurry.
  • the series of operations was carried out in the glovebox under argon atmosphere.
  • Li 2 S:P 2 S 5 :SiS 2 :LiCl was 6.45:1:2:0.40.
  • the obtained slurry was dried under vacuum at 180° C. for 4 hours to remove the solvent. Removal of the solvent was carried out while stirring the solution. After that, it was cooled to room temperature to obtain a precursor.
  • the obtained precursor was put into a glass reaction tube, which was placed in an electric tube furnace in a manner such that the precursor was not exposed to atmosphere.
  • Argon (G3 grade) was injected into the reaction tube, the temperature was increased to 475° C. over 3 hours, and then burning was carried out at 475° C. for 8 hours, thereby synthesizing Li 3.355 Si 0.505 P 0.505 S 3.9 Cl 0.1 crystal.
  • Li 2 S manufactured by Sigma-Aldrich, purity: 99.8%
  • P 2 S 5 manufactured by Sigma-Aldrich, purity: 99%
  • Li—P—S Li—P—S homogeneous solution
  • Li 2 S was added in an amount of 2 times the molar quantity of P 2 S 5 , and stirring was carried out for 6 hours to cause precipitation of Li 3 PS 4 , thereby obtaining an Li 3 PS 4 -containing slurry.
  • Li 3 PS 4 -containing slurry 8.57 g of the Li 3 PS 4 -containing slurry was mixed with 23.30 g of the Li—Si—S homogeneous solution so that the molar ratio of Si:P became 1:1 to prepare a mixed slurry. Further, to the obtained mixed slurry, 51.9 mg of LiCl (manufactured by Sigma-Aldrich, purity: 99.99%), wherein the amount thereof was 0.40 time the molar quantity of P 2 S 5 in the mixed slurry, was added while stirring, and mixing was carried out at room temperature for 3 hours.
  • LiCl manufactured by Sigma-Aldrich, purity: 99.99%
  • Li 2 S Li 2 S was added while stirring so that the amount thereof became 6.45 times the molar quantity of P 2 S 5 , and mixing was carried out at room temperature for 12 hours to prepare a slurry.
  • the series of operations was carried out in the glovebox under argon atmosphere.
  • Li 2 S:P 2 S 5 :SiS 2 :LiCl was 6.45:1:2:0.40.
  • the obtained slurry was dried under vacuum at 180° C. for 4 hours to remove the solvent. Removal of the solvent was carried out while stirring the solution. After that, it was cooled to room temperature to obtain a precursor.
  • the obtained precursor was put into a glass reaction tube, which was placed in an electric tube furnace in a manner such that the precursor was not exposed to atmosphere.
  • Argon (G3 grade) was injected into the reaction tube, the temperature was increased to 475° C. over 3 hours, and then burning was carried out at 475° C. for 8 hours, thereby synthesizing Li 3.355 Si 0.505 P 0.505 S 3.9 Cl 0.1 crystal.
  • Li—P—S homogeneous solution 498 mg of SiS 2 (manufactured by Mitsuwa Chemicals Co., Ltd.) was added while stirring so that the amount thereof became 1.64 times the molar quantity of P 2 S 5 in the Li—P—S homogeneous solution, and mixing was carried out at room temperature for 12 hours. Further, to the above-described homogeneous solution, 799 mg of Li 2 S was added while stirring so that the amount thereof became 6.27 times the molar quantity of P 2 S 5 in the homogeneous solution, and mixing was carried out at room temperature for 24 hours to obtain a slurry. The series of operations was carried out in the glovebox under argon atmosphere. Regarding the molar ratio of all the raw materials added to the system, Li 2 S:P 2 S 5 :SiS 2 was 6.27:1:1.64.
  • the obtained slurry was dried under vacuum at 180° C. for 2 hours to remove the solvent. Removal of the solvent was carried out while stirring the solution. After that, it was cooled to room temperature to obtain a precursor.
  • the obtained precursor was put into a glass reaction tube, which was placed in an electric tube furnace in a manner such that the precursor was not exposed to atmosphere.
  • Argon (G3 grade) was injected into the reaction tube, the temperature was increased to 550° C. over 3 hours, and then burning was carried out at 550° C. for 8 hours, thereby synthesizing Li 3.45 Si 0.45 P 0.55 S 4 crystal.
  • Each of the sulfide-based solid electrolytes obtained in Examples 1-3 and Comparative Example 1 was subjected to uniaxial molding (420 MPa) to obtain a disk having a thickness of about 1 mm and a diameter of 10 mm.
  • the AC impedance was measured by the four-terminal method utilizing an indium electrode at room temperature (25° C.) (“SI1260 IMPEDANCE/GAIN-PHASE ANALYZER” manufactured by Solartron), and the lithium ion conductivity was calculated.
  • the sample was put into a thermostatic bath with its temperature being set at 25° C. and it was kept for 30 minutes, and after that, the lithium ion conductivity was measured.
  • the measurement frequency range was 0.1 Hz to 1 MHz, and the amplitude was 50 mV.
  • the measurement results of the lithium ion conductivity are shown in Table 1 below.
  • the obtained filter residue and white solid were subjected to the SEM-EDX measurement (scanning electron microscope “S-3400N” manufactured by Hitachi High-Technologies Corporation, acceleration voltage: 5.0 kV at the time of surface observation and 15.0 kV at the time of EDX) under vacuum conditions at room temperature (25° C.).
  • SEM-EDX measurement scanning electron microscope “S-3400N” manufactured by Hitachi High-Technologies Corporation, acceleration voltage: 5.0 kV at the time of surface observation and 15.0 kV at the time of EDX
  • Table 2 and Table 3 As shown in Table 2 and Table 3, the amount of oxygen in the white solid that is a filtrate-dried product was smaller than that in the filter residue, and it is considered that an oxygen-containing compound was successfully removed by filtration.
  • FIG. 4 The results of the X-ray diffraction measurement of the obtained filter residue and white solid are shown in FIG. 4 .
  • FIG. 4 in the case of the filter residue, peaks of metal Si as an impurity were observed. Meanwhile, in the case of the white solid obtained by drying the filtrate, peaks of impurities were not observed. Accordingly, it is considered that metal Si was successfully removed by filtration.

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